T Compiler Meeting Agenda 2022 09 15

T-compiler Meeting Agenda 2022-09-15

Announcements

Other WG meetings

MCPs/FCPs

  • New MCPs (take a look, see if you like them!)
  • Old MCPs (not seconded, take a look)
    • “Arbitrary annotations in compiletest” compiler-team#513 (last review activity: 4 months ago)
    • “Add #[alias] attribute to allow symbol aliasing” compiler-team#526 (last review activity: about 54 days ago)
    • “Use RangeInclusive in SpanData instead of lo/hi” compiler-team#534 (last review activity: about 19 days ago)
    • “Allow informational -Z flags on stable compiler” compiler-team#542 (last review activity: about 19 days ago)
    • " Promote i586-unknown-linux-gnu to Tier 2 with Host Tools " compiler-team#543 (last review activity: about 19 days ago)
    • “Lower baseline expectations for i686 unix-like targets” compiler-team#548 (last review activity: about 6 days ago)
    • “MCP: Flag to disable extended error info.” compiler-team#550 (last review activity: about 6 days ago)
    • “New Tier-3 target proposal: powerpc64-ibm-aix” compiler-team#553 (last review activity: about 6 days ago)
    • “configurable rustc timeout for compiletest tests” compiler-team#554 (last review activity: about 6 days ago)
    • “MCP: Raise UEFI Targets to Tier-2” compiler-team#555 (last review activity: about 5 days ago)
    • “Raise minimum supported macOS and iOS versions” compiler-team#556 (last review activity: about 5 days ago)
  • Pending FCP requests (check your boxes!)
    • No pending FCP requests this time.
  • Things in FCP (make sure you’re good with it)
    • No FCP requests this time.
  • Accepted MCPs
    • No new accepted proposals this time.
  • Finalized FCPs (disposition merge)
    • “Tracking issue for ..X, and ..=X (#![feature(half_open_range_patterns)])” rust#67264
    • “Tracking Issue for #[instruction_set] attribute (RFC 2867)” rust#74727
    • “Consider #[must_use] annotation on async fn as also affecting the Future::Output” rust#100633

WG checkins

  • Generic Associated Types initiative by @Jack Huey (previous checkin):

    After much discussion, the GATs stabilization PR has been merged and is on track to stabilize in the next release. The document PR is pending.

  • @_WG-diagnostics by @Esteban Küber and @oli (previous checkin):

    Progress remains steady in the migration to the translation machinery. Lots of first-time contributions. Big thanks to @davidtwco for leading this effort. Tons of smaller improvements around structured suggestions.

Backport nominations

T-compiler beta / T-compiler stable

  • :beta: “Fix code generation of Rvalue::Repeat with 128 bit values” rust#101612
  • No stable nominations for T-compiler this time.

T-rustdoc beta / T-rustdoc stable

  • No backport nominations for T-rustdoc this time.

:back: / :shrug: / :hand:

PRs S-waiting-on-team

T-compiler

  • 3 PRs hidden as S-blocked on other teams
  • “Empty iterator error” rust#100751
    • nominated for T-compiler discussion by @fee1-dead

Oldest PRs waiting for review

T-compiler

  • “[DO NOT MERGE] Add ballast to some important AST types.” rust#100044 (last review activity: about 43 days ago)
    • This is a perf. experiment from @nnethercote
  • “More distinctive pretty-printing of function item types” rust#99927 (last review activity: about 41 days ago)
    • assigned reviewer @Esteban Küber
  • “super_relate_consts: stop being generic” rust#100016 (last review activity: about 37 days ago)
    • unsure about the status cc @lcnr @Jack Huey
  • “fix universe map in ifcx.instantiate_canonical_*” rust#99814 (last review activity: about 37 days ago)
    • @nikomatsakis was mentioned as additional reviewer
  • “Added support for PlayStation Vita” rust#90584
    • last comment from Wesley: waiting for progress on policy in #88991 (now merged, see comment)
    • what is the current status? Does it need an official MCP (author replied to tier 3 MCP questions)

Issues of Note

Short Summary

P-critical

T-compiler

  • “Regression in consteval: error[E0080]: could not evaluate static initializer (unable to turn pointer into raw bytes)” rust#99923
  • “Potential miscompilation on i686 of chacha20” rust#101346
    • discussed last week, Felix left some comments, unclear if replied in full
    • can close issue?
  • “Wrong cast of u16 to usize on aarch64” rust#97463

T-rustdoc

  • No P-critical issues for T-rustdoc this time.

P-high regressions

P-high beta regressions

  • “Anon lifetime in impl Trait no longer suggests adding a lifetime parameter” rust#100615
  • “Borrow checking for static methods became more strict” rust#100725

Unassigned P-high nightly regressions

Performance logs

triage logs for 2022-09-13

From the viewpoint of metrics gathering, this was an absolutely terrible week, because the vast majority of this week’s report is dominated by noise. Several benchmarks (html5ever, cranelift-codegen, and keccak) have all been exhibiting bimodal behavior where their compile-times would regress and improve randomly from run to run. Looking past that, we had one small win from adding an inline directive.

Triage done by @pnkfelix. Revision range: e7cdd4c0..17cbdfd0

Summary:

(instructions:u) mean range count
Regressions (primary) 1.1% [0.2%, 6.2%] 26
Regressions (secondary) 1.9% [0.1%, 5.6%] 34
Improvements (primary) -1.8% [-29.4%, -0.2%] 42
Improvements (secondary) -1.3% [-5.3%, -0.2%] 50
All (primary) -0.7% [-29.4%, 6.2%] 68

11 Regressions, 11 Improvements, 13 Mixed; 11 of them in rollups 30 Untriaged Pull Requests 71 artifact comparisons made in total

Regressions

Simplify hir::PathSegment #101228 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.7% [0.3%, 1.3%] 16
Regressions (secondary) 1.3% [0.9%, 1.8%] 14
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.7% [0.3%, 1.3%] 16
  • already triaged as “these regressions aren’t real; they are an artifact of some current bimodality”

Rollup of 7 pull requests #101485 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.9% [0.3%, 1.6%] 15
Regressions (secondary) 1.2% [0.8%, 1.6%] 9
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.9% [0.3%, 1.6%] 15
  • already triaged as “these regressions aren’t real; they are an artifact of some current bimodality”

Track PGO profiles in depinfo #100801 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) 2.0% [1.8%, 2.4%] 6
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) - - 0
  • already triaged as “these regressions aren’t real; they are an artifact of some current bimodality”

Make HandleCycleError an enum instead of a macro-generated closure #101303 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.2% [1.1%, 1.3%] 2
Regressions (secondary) 3.4% [3.1%, 3.9%] 6
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 1.2% [1.1%, 1.3%] 2
  • already triaged as “these regressions aren’t real; they are an artifact of some current bimodality”

Shrink hir::Ty and hir::Pat #101467 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.8%, 1.0%] 6
Regressions (secondary) 7.5% [7.5%, 7.5%] 1
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.8% [0.8%, 1.0%] 6

Normalize before erasing late-bound regions in equal_up_to_regions #101437 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.2% [1.1%, 1.3%] 2
Regressions (secondary) 3.4% [3.0%, 3.9%] 6
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 1.2% [1.1%, 1.3%] 2
  • already triaged as noise; cranelift-codegen and keccak have been noisy lately.

Rollup of 6 pull requests #101639 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.3% [1.2%, 1.4%] 2
Regressions (secondary) 3.1% [0.8%, 4.0%] 8
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 1.3% [1.2%, 1.4%] 2

Only compute captures once when building MIR. #100968 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.2% [1.1%, 1.3%] 2
Regressions (secondary) 3.4% [3.1%, 3.9%] 6
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 1.2% [1.1%, 1.3%] 2

Fix LLVM IR type mismatch reported in #99551 #101647 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.3% [1.3%, 1.3%] 1
Regressions (secondary) 3.4% [3.1%, 3.9%] 6
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 1.3% [1.3%, 1.3%] 1

Simplify codeblock and their associated tooltip #101613 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.3% [1.3%, 1.3%] 1
Regressions (secondary) 3.4% [3.1%, 3.9%] 6
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 1.3% [1.3%, 1.3%] 1

Compute information about function parameters on THIR #101086 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.4% [0.2%, 0.5%] 10
Regressions (secondary) 0.6% [0.3%, 1.6%] 4
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.4% [0.2%, 0.5%] 10
  • between 0.38% and 0.47% regression for stm32f4 in various incremental scenarios. Approximately 0.25% on serde,clap,image for incremental.
  • it seems plausible that this is just overhead that we have to pay, in terms of adding more state to the THIR, in exchange for simpler MIR construction code.
  • (its also possible that this is just noise, though the listed benchmarks are not the same as the other ones that have been exhibiting bimodality this last week.)
  • marking as triaged.

Improvements

Inline <T as From<T>>::from #100733 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.8% [-2.2%, -0.2%] 25
Improvements (secondary) -1.4% [-2.2%, -0.5%] 22
All (primary) -0.8% [-2.2%, -0.2%] 25

Rollup of 8 pull requests #101508 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -1.2% [-1.3%, -1.1%] 2
Improvements (secondary) -3.3% [-3.8%, -2.9%] 6
All (primary) -1.2% [-1.3%, -1.1%] 2
  • (bimodality in other direction, cranelift-codegen and keccak)

Lower the assume intrinsic to a MIR statement #98332 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.8% [-0.9%, -0.7%] 6
Improvements (secondary) - - 0
All (primary) -0.8% [-0.9%, -0.7%] 6
  • presume bimodality in other direction for html5ever

Update miri submodule #101522 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.8% [-0.9%, -0.7%] 6
Improvements (secondary) - - 0
All (primary) -0.8% [-0.9%, -0.7%] 6
  • presume bimodality in other direction for html5ever

Rollup of 14 pull requests #101544 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -1.2% [-1.3%, -1.1%] 2
Improvements (secondary) -3.3% [-3.8%, -3.0%] 6
All (primary) -1.2% [-1.3%, -1.1%] 2
  • (bimodality in other direction, cranelift-codegen and keccak)

const_generics: correctly deal with bound variables #98900 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.9% [-1.3%, -0.8%] 8
Improvements (secondary) -3.3% [-3.8%, -2.9%] 6
All (primary) -0.9% [-1.3%, -0.8%] 8
  • (bimodality in other direction, html5ever, cranelift-codegen, and keccak)

Rollup of 7 pull requests #101577 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -1.1% [-1.1%, -1.1%] 1
Improvements (secondary) -7.5% [-7.5%, -7.5%] 1
All (primary) -1.1% [-1.1%, -1.1%] 1

Rollup of 6 pull requests #101603 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -1.3% [-1.4%, -1.2%] 2
Improvements (secondary) -3.3% [-3.8%, -2.8%] 7
All (primary) -1.3% [-1.4%, -1.2%] 2
  • (bimodality in other direction, cranelift-codegen, keccak, and coercions)

Rollup of 6 pull requests #101652 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-1.3%, -0.2%] 7
Improvements (secondary) -2.6% [-3.8%, -0.4%] 8
All (primary) -0.4% [-1.3%, -0.2%] 7
  • largely cranelift-codegen, keccak

Remove ReEmpty #98559 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.7% [-1.3%, -0.3%] 5
Improvements (secondary) -3.3% [-3.8%, -3.0%] 6
All (primary) -0.7% [-1.3%, -0.3%] 5
  • largely cranelift-codegen, keccak

Make compare_predicate_entailment no longer a query #101615 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-0.5%, -0.4%] 6
Improvements (secondary) -0.4% [-0.5%, -0.3%] 5
All (primary) -0.4% [-0.5%, -0.4%] 6

Mixed

Make const_eval_select a real intrinsic #100759 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.3%, 1.4%] 12
Regressions (secondary) 2.4% [0.2%, 4.1%] 9
Improvements (primary) -1.2% [-3.0%, -0.6%] 7
Improvements (secondary) -1.4% [-1.6%, -1.0%] 10
All (primary) 0.1% [-3.0%, 1.4%] 19
  • If you take html5ever, cranelift-codegen, keccak out of the mix here, …
  • … you are left with the following four primary regressions: ripgrep by 1.37%, clap by 1.34%, cargo by 0.80%, serde_derive by 0.33%.
  • The regression to ripgrep does look like it might be legitimate, at least from skimming its graph and zooming in.

proc_macro/bridge: use the cross-thread executor for nested proc-macros #101414 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.9% [0.4%, 1.4%] 10
Regressions (secondary) 1.1% [0.6%, 1.7%] 9
Improvements (primary) -1.2% [-1.3%, -1.2%] 2
Improvements (secondary) -3.4% [-3.9%, -3.0%] 6
All (primary) 0.5% [-1.3%, 1.4%] 12

Rollup of 6 pull requests #101439 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.9% [0.9%, 1.0%] 2
Regressions (secondary) 2.1% [1.8%, 2.4%] 6
Improvements (primary) -2.9% [-29.7%, -0.3%] 18
Improvements (secondary) -1.2% [-1.8%, -0.7%] 9
All (primary) -2.5% [-29.7%, 1.0%] 20
  • the regressions flagged here are almost certainly noise from recently arising bimodality in certain benchmarks.
  • already marked as triaged

Rollup of 7 pull requests #101464 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) 1.6% [1.6%, 1.6%] 1
Improvements (primary) -0.8% [-1.3%, -0.3%] 13
Improvements (secondary) -1.3% [-1.7%, -0.8%] 8
All (primary) -0.8% [-1.3%, -0.3%] 13

Rollup of 5 pull requests #101479 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.9% [0.4%, 1.3%] 10
Regressions (secondary) 1.3% [0.8%, 1.8%] 8
Improvements (primary) - - 0
Improvements (secondary) -1.4% [-1.6%, -1.2%] 6
All (primary) 0.9% [0.4%, 1.3%] 10

change stdlib circular dependencies handling #100404 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.2% [1.1%, 1.3%] 2
Regressions (secondary) 3.4% [3.0%, 3.9%] 6
Improvements (primary) -0.8% [-0.9%, -0.7%] 6
Improvements (secondary) -1.0% [-1.0%, -1.0%] 1
All (primary) -0.3% [-0.9%, 1.3%] 8

Add test for #98294 #101232 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.7%, 0.9%] 6
Regressions (secondary) - - 0
Improvements (primary) - - 0
Improvements (secondary) -1.1% [-1.1%, -1.1%] 1
All (primary) 0.8% [0.7%, 0.9%] 6

Shrink PredicateS #101432 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.7%, 0.9%] 6
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-0.5%, -0.4%] 5
Improvements (secondary) -1.4% [-1.4%, -1.4%] 1
All (primary) 0.2% [-0.5%, 0.9%] 11

Use niche-filling optimization even when multiple variants have data. #94075 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 3.2% [0.8%, 9.4%] 5
Regressions (secondary) 1.8% [0.2%, 5.2%] 27
Improvements (primary) -0.6% [-1.1%, -0.2%] 23
Improvements (secondary) -1.5% [-2.9%, -0.2%] 16
All (primary) 0.1% [-1.1%, 9.4%] 28

The syn regression sounds bad. Left a comment.

Rollup of 7 pull requests #101592 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) 4.6% [4.6%, 4.6%] 1
Improvements (primary) -1.2% [-1.3%, -1.1%] 2
Improvements (secondary) -3.3% [-3.8%, -2.9%] 6
All (primary) -1.2% [-1.3%, -1.1%] 2
  • Already triaged saying “The coercions regression is only for a single profile/scenario combination, so I don’t think it’s meaningful.”

Initial implementation of return-position impl Trait in traits #101224 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.5% [0.2%, 1.4%] 19
Regressions (secondary) 2.0% [0.2%, 4.1%] 13
Improvements (primary) -0.9% [-1.1%, -0.8%] 6
Improvements (secondary) -0.3% [-0.3%, -0.3%] 1
All (primary) 0.2% [-1.1%, 1.4%] 25
  • Many of regressions fall in the bimodal noise category.
  • The serde regression did not, but it is addressed by the follow-up PR #101615
  • Marking as triaged.

Update LLVM used in x86 CI dist builds to 15.0.0 #101527 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) 1.3% [1.3%, 1.3%] 1
Improvements (primary) -0.6% [-0.8%, -0.5%] 12
Improvements (secondary) -0.5% [-0.6%, -0.3%] 4
All (primary) -0.6% [-0.8%, -0.5%] 12

The <*const T>::guaranteed_* methods now return an option for the unknown case #101483 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.4% [0.2%, 0.6%] 5
Regressions (secondary) - - 0
Improvements (primary) -1.1% [-1.4%, -0.9%] 5
Improvements (secondary) -2.9% [-3.8%, -0.7%] 8
All (primary) -0.4% [-1.4%, 0.6%] 10
  • The big improvements are just noise from some bimodal behavior we’ve been observing this week.
  • Its possible that there was some regression to cargo here, but I don’t think the data shows it to be large enough to be worth investigating. (I admit, my attitude there might be colored by my frustration with the huge noise impact of the aforementioned bimodality on all of the perf results from the last week.)
  • marked as triaged

Nominated Issues

T-compiler

  • “Empty iterator error” rust#100751
    • @Vadim Petrochenkov nominated (comment)
  • “Random lifetime may not life long enough from other part of the code” rust#96645
    • @Esteban Küber nominated for awareness of a latent bug or regression in incr-comp with nll borrowck (comment)

RFC

  • No nominated RFCs for T-compiler this time.

Next week’s WG checkins

  • @_WG-rustc-dev-guide by @Santiago Pastorino and @Yuki Okushi|217081
  • Impl Trait initiative by @oli